I know that 了 after a verb means a completion or termination of a certain action, such as:

吃飽了
(I am) full.

開始了
(It) has started.

不動了
(It) is not moving anymore.

But what about 了 in 忘不了 and 喝不了? Is 不了 an expression, or does each character have a specific meaning in this context? How would 忘不了 and 喝不了 be translated? (I suppose it would not be I have not forgotten yet and I have not drunk yet...)